Term classical economics assumptions Definition: Classical economics, especially as directed toward macroeconomics, relies on three key assumptions--flexible prices, Say's law, and saving-investment equality. Flexible prices ensure that markets adjust to equilibrium and eliminate shortages and surpluses. Say's law states that supply creates its own demand and means that enough income is generated by production to purchase the resulting production. The saving-investment equality ensures that any income leaked from consumption into saving is replaced by an equal amount of investment. Although of questionable realism, these three assumptions imply that the economy would operate at full employment.